In vehicles with a regenerative brake (electric and hybrid vehicles), a major part of the braking power or the total braking power is generated by the electric drive when working on generator in the partial braking range, and the recuperated energy is fed back into the battery. To achieve a high efficiency, the total braking power is generated by the generator, if possible, and thus applied only to the driven axle. On a low coefficient of friction, such as on ice, this may initiate ABS control because the coefficient of friction on the driven axle is not sufficient to transmit the required brake torque. When the ABS system is active, the regenerative brake is switched off to uncouple the wheels from the driving track and safeguard the normal ABS function.
In the following, the example is based on a vehicle with electric or electro-hybrid drive (electric and combustion engine) and EHB (electro-hydraulic) brake.
The following problems are encountered in practical operations:
When the ABS control is terminated, it would be favorable to readmit the regenerative brake. However, this would shift the total braking power to the driving axle again, and permanent cycles (cyclic change-over ABS—regenerative brake—ABS—etc.) could occur. This condition is felt to be unpleasant by the driver and has adverse effects on driving stability.
DE 198 42 472 A1 discloses a vehicle brake system with friction devices and regenerative brake devices. In this arrangement, the regenerative brake is disconnected upon entry into ABS control. It stays disconnected until the braking operation is completed. This condition is detected by the fact that the driver accelerates or releases the brake during standstill.